As one of the control methods of internal combustion engines, there is known torque demand control which determines a manipulation variable of each actuator with torque as a control variable. Japanese Patent Application Laid-Open No. 2010-053705 describes one example of the control device which performs torque demand control. The control device, which is described in Japanese Patent Application Laid-Open No. 2010-053705, performs torque control by control of a cylinder intake air quantity by a throttle, and control of ignition timing by an ignition device. In more detail, the control device determines a target air quantity based on required torque, determines a throttle opening from the target air quantity, calculates estimated torque which is realized under optimal ignition timing based on the present throttle opening, and determines the ignition timing based on the ratio of the required torque and the estimated torque.
The required torque for an internal combustion engine includes required torque which is required by a driver via accelerator pedal manipulation (hereinafter, driver required torque), and required torque (hereinafter, control device required torque) which the control devices of a vehicle such as an ECT (Electronic controlled transmission) and a TRC (Traction Control System). The driver required torque is the basis of the required torque, and the control device required torque is added to it in accordance with necessity in vehicle control. These two kinds of required torque clearly differ from each other in the change speed thereof. The driver required torque basically has a signal with a low change speed, which changes at a speed corresponding to the acceleration manipulation of a driver, whereas the control device required torque has a signal with a high change speed, which abruptly changes the torque which is outputted by an internal combustion engine instantly and temporarily.
According to the control device which performs torque demand control as described in Japanese Patent Laid-Open No. 2010-053705, required torque can be realized with high precision even when the control device required torque with a high change speed is included therein. Hereinafter, this point will be described in detail with use of FIGS. 6, 7 and 8.
FIG. 6 is a functional block diagram showing a configuration of a control device which performs torque demand control which is conventionally proposed. The control device which is described in Japanese Patent Laid-Open No. 2010-053705 is also substantially configured as shown in FIG. 6. The control device shown in FIG. 6 sets a throttle 102 and an ignition device 104 as the objects to be manipulated. The control device includes a required torque determining section 110, a required efficiency determining section 112, an air quantity control target torque calculating section 114, a target torque calculating section 116, a throttle opening calculating section 118, a combustion ensuring section 120, an estimated torque calculating section 122, a target efficiency calculating section 124, a combustion ensuring section 126 and an ignition timing calculating section 128.
In the required torque determining section 110, required torque (TQrq) to the internal combustion engine is determined. The required torque includes driver required torque and control device required torque as described above. In the required efficiency determining section 112, a required efficiency (ηrq) to the internal combustion engine is determined. The required torque and the required efficiency are inputted in the air quantity control target torque calculating section 114. In the air quantity control target torque calculating section 114, air quantity control target torque (TQt) is calculated by dividing the required torque by the required efficiency. However, concerning the required efficiency, a required efficiency (ηrq1) which is processed in the combustion ensuring section 120 is inputted in the air quantity control target torque calculating section 114. In the combustion ensuring section 120, the minimum value of the required efficiency which is used in calculation of the air quantity control target torque is restricted by a combustion limit guard. The air quantity control target torque is inputted in the target air quantity calculating section 116, and is converted into a target air quantity (KLt) with use of a torque-air quantity conversion map. The target air quantity is inputted in the throttle opening calculating section 118, and is converted into a target throttle opening (TAt) with use of an air inverse model. The throttle 2 is operated in accordance with the target throttle opening.
In the estimated torque calculating section 122, calculation of estimated torque (TQmbt) based on a present throttle opening (TAact) is performed. The estimated torque is inputted in the target efficiency calculating section 124 together with the required torque which is determined in the required torque determining section 110. In the target efficiency calculating section 124, a ratio of the required torque to the estimated torque is calculated as a target efficiency (ηsa) for controlling ignition timing. The target efficiency is processed in the combustion ensuring section 126, and a target efficiency (ηsa1) after processing is inputted in the ignition timing calculating section 128. In the combustion ensuring section 126, the minimum value of the target efficiency which is used in calculation of the ignition timing is restricted by the combustion limit guard. The value of the combustion limit guard which is set in the combustion ensuring section 126 for the required efficiency is the same value as the value of the combustion limit guard which is set in the combustion ensuring section 120 for the target efficiency. In the ignition timing calculating section 128, target ignition timing (SAt) is calculated based on the target efficiency. The ignition device 4 is manipulated in accordance with the target ignition timing. The target ignition timing is set at optimal ignition timing when the value of the target efficiency is 1, and as the value of the target efficiency is smaller than 1, the target ignition timing is retarded more from the optimal ignition timing.
FIGS. 7 and 8 are charts showing the operations of the internal combustion engine, which are realized by the control device of the configuration shown in FIG. 6. First, the operation shown in FIG. 7 will be described.
In the chart of FIG. 7, the ECT required torque which is one kind of the control device required torque is outputted in addition to the driver required torque. The signal of the ECT required torque is set as a rectangular signal so as to reduce the torque, which is outputted by the internal combustion engine, temporarily and instantly. Further, in agreement with the rectangular signal of the ECT required torque, the rectangular signal of a value smaller than 1 which is a reference value is also outputted in the required efficiency. The signal of the required efficiency which is outputted at this time is regulated so that the value of the air quantity control target torque which is obtained by dividing the required torque by the required efficiency becomes constant.
As a result that such signals of the required torque and the required efficiency are outputted, the air quantity control target torque is kept constant irrespective of change of the required torque. As a result, the throttle opening is not changed in correspondence with the waveform of the ECT required torque, and the cylinder intake air quantity is kept constant. Meanwhile, the target efficiency for ignition timing control which is obtained by dividing the required torque by the estimated torque changes rectangularly in correspondence with the waveform of the ECT required torque. The target efficiency becomes lower than 1 which is the reference value, whereby the ignition timing is retarded from MBT, and in association with this, the generated torque is reduced. The responsiveness of the change of the torque to the change of the ignition timing is high, and therefore, the generated torque shows a rectangular change similar to that of the required torque.
The operation of the control device which is described above is the operation in the case in which the required efficiency and the target efficiency for ignition timing control become the values higher than the combustion limit guard. When they become the values lower than the combustion limit guard, the operation of the control device is as shown in the chart of FIG. 8. Hereinafter, the operation shown in FIG. 8 will be described.
The target efficiency for ignition timing control is calculated based on the required torque. Therefore, when the reduction amount of the ECT required torque included in the required torque is large, the reduction amount of the target efficiency from the reference value also becomes large, and the target efficiency (ηsa) falls below the combustion limit guard. In this case, the target efficiency (ηsa1) which is restricted by the combustion limit guard is used in calculation of the ignition timing, and therefore, the ignition timing is restricted by the retard limit at which optimal combustion can be ensured. When a restriction is placed on the retard amount of the ignition timing as above, the required torque cannot be realized with high efficiency with only the retard of the ignition timing.
However, when the reduction amount of the ECT required torque from the reference value is large, the reduction amount of the required efficiency which is outputted in correspondence with the ECT required torque also becomes large. For calculation of the air quantity control target torque as a result that the required efficiency (ηrq) falls below the combustion limit guard, the required efficiency (ηrq1) which is restricted by the combustion limit guard is used. Therefore, the air control target torque does not become constant, and shows a rectangular change corresponding to the ratio of ηrq1 and ηrq. As a result, the throttle opening is also changed in correspondence with the waveform of the air quantity control target torque, and the cylinder intake air quantity is temporarily reduced. Thereby, the generated torque shows the same change as the required torque. More specifically, according to the operation shown in FIG. 8, the insufficient amount of the torque reduction amount which occurs by the retard amount of the ignition timing being restricted is ensured by decreasing the cylinder intake air quantity by operating the throttle in a closed direction.
As described above, according to the control device of the configuration shown in FIG. 6, the throttle 102 and the ignition device 104 are cooperatively manipulated in accordance with the content of the required torque. Thereby, even when the control device required torque with a high change speed like the ECT required torque is included, the required torque can be realized with high precision.
Incidentally, the aforementioned torque demand control can be applied to control of the internal combustion engines including a turbo supercharger and a mechanical supercharger. However, when the internal combustion engines with superchargers include actuators which actively change a supercharging pressure, for example, a waste gate valve and a variable nozzle, an electric motor which drives a compressor, or the like, manipulation of these actuators needs to be considered. This is because depending on the way of manipulation of these actuators, control precision of the torque is likely to be impaired as will be described as follows.
In the aforementioned torque demand control, the generated torque is controlled by cooperatively controlling the cylinder intake air quantity and the ignition timing, and the cylinder intake air quantity is controlled by the throttle. The flow rate of the air which passes through the throttle is changed by manipulating the throttle and changing the opening thereof, whereby the cylinder intake air quantity can be controlled. However, the throttle passing flow rate also depends on the pressure difference before and after the throttle, and therefore, when the actuators such as a waste gate value and a variable nozzle are present, the cylinder intake air quantity cannot be controlled with high precision unless manipulation of them is not optimal. Accordingly, when the aforementioned torque demand control is applied to an internal combustion engine with a supercharger, it becomes a problem how to manipulate the actuator which actively changes a supercharging pressure and the throttle cooperatively.